Spark is a Swiss Army Knife of a hadoop stack. It makes glue between tools and is a de-facto interface for them.

Spark has a lot of advantages:

• it's a wonderfull connector: if you look at a way to connect to a tool, spark already has a connector for you. Special mention to csv: spark is also able to read multilined csv with quote, empty lines and special character in it.
• it can manipulate very huge dataset: in case the dataset does not feat in memory, the spark partitionning feature allows spliting the tasks in working pipelines
• its parallel feature can take advantage of a hadoop cluster, but is a great solution for a laptop too
• the scala spark-shell is really handy for development. It's auto-completion features are superior to any shell I've dealt with before
• it has SQL syntax, SPARKQL compliance, and also machine learning distributed implementation.
• it can be programmed in scala, python, R, java and julia.

Spark as some disadvantages:

• time of writing, spark does not support hive ACID tables. The workaround is to do a major compaction of the table before reading it with spark. This means it cannot yet be integrated into a hive ETL process based on ACID tables.
• spark programming needs a lot of skills. It is then not a good choice for intermediate enterprise in comparison to hive programming. Again, hive ETL looks a better fit for a maintainability reason.